Line following robot acting weirdly

i made a line following robot ,used pid control algorithm ,tuned it properly for a black line with white background,it worked properly,but when i changed it to white line over black background ,it follows the line but moves in a zig zag manner,both the tracks r the same with the same track width.

the only thing i changed was from this

unsigned int pos = qtra.readLine(sensors);

to this

 unsigned int pos = qtra.readLine(sensors,QTR_EMITTERS_ON,1 );

please help …urgent…have competition day after

thankyou

Hello.

I am sorry you are having trouble with your QTR sensors. Can you try printing or recording the values you are getting for qtra.readLine() while running both your black line following and white line following code? Have you recalibrated your QTR sensors with the white line on black background?

-Jon

the values r the reverse and the position shown is also right …i calibrate the sensors every time i run it …

Like I mentioned in my initial response, can you post the values you are getting for qtra.readLine() while running both your black line following and white line following code? I would like to see how those values compare.

Can you also post a video of the behavior and the full code you are using?

-Jon

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